Antenna system for narrowband communications systems and method of operation

ABSTRACT

There is disclosed an improved base station for communicating with communication units in a wireless messaging system. According to an advantageous embodiment, the base station comprises: 1) a transmitter that is capable of transmitting messages to the communication units in a forward-channel having a first frequency range; 2) a receiver that is capable of receiving messages from the communication units in a reverse-channel having a second frequency range; and 3) an antenna that is capable of transmitting the forward-channel messages at a first angle of electrical downtilt below the horizon and receiving the reverse-channel messages at a second angle of electrical downtilt, wherein the second angle of electrical downtilt is less than the first angle of electrical downtilt.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of prior U.S. application Ser. No.09/002,191, filed on Dec. 31, 1997 now U.S. Pat. No. 6,097,970, entitled“ANTENNA SYSTEM FOR NARROWBAND COMMUNICATIONS SYSTEMS AND METHOD OFOPERATION,” which is also assigned to the assignee of the presentinvention. The invention disclosed in this application is related tothat disclosed in U.S. patent application Ser. No. 09/001,759, alsofiled on Dec. 31, 1997, entitled “SYSTEM FOR SCHEDULING REVERSE-CHANNELMESSAGES IN NARROWBAND COMMUNICATIONS SYSTEMS AND METHOD OF OPERATION,”which is also assigned to the assignee of the present invention. Thedisclosures of these related patent applications are incorporated hereinby reference for all purposes as if fully set forth herein.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to wireless communicationsystems and methods of operating the same, and, in particular, tonarrowband communication systems for one-way and two-way transmission ofvoice and data messages.

BACKGROUND OF THE INVENTION

The demand for better and cheaper wireless telecommunication servicesand equipment continues to grow at a rapid pace. Much of this growth isspurred by the Federal Communication Commission's (“FCC”) approval ofcertain frequency bands for the next generation of PersonalCommunication Service (“PCS”) devices that provide voice telephoneservice as well as advanced voice and/or data message paging services. Arelatively small portion of the available spectrum was set aside fornarrowband PCS, which is more suited to advanced message pagingservices, to encourage efficient use of the available spectrum.

There are a number of well-known wireless communication techniques thatattempt to maximize the efficiency with which the available spectrum isused. These methods include frequency division multiple access (“FDMA”),time division multiple access (“TDMA”), code division multiple access(“CDMA”), and the like. The term “multiple access” means that multiple,simultaneous users (or “subscribers”) are supported in each of thesesystems.

In an FDMA system, for instance, the total available radio spectrum isdivided into separate frequency bands (or “channels”) of, for example,25-30 KHz for those systems based on the “AMPS” or “TACS” standards, or10 KHz for newer systems, such the narrowband PCS (“NPCS”) advancedmessaging systems. In FDMA, only one subscriber at a time is assigned toa channel. No other subscriber may access this channel until thetransmission of the message sent by the first subscriber is completed.

In a TDMA system, the total available radio spectrum is again dividedinto separate frequency bands. Each band is then temporally subdividedinto, for example, three time slots. Only one subscriber at a time isassigned to each channel, where a channel corresponds to a particularfrequency band and a particular time slot for that band. No othersubscriber may access this channel until the transmission of the messagesent by the first subscriber is completed.

In a CDMA system, the total available radio spectrum is used by eachsubscriber. Each subscriber transmits a unique, pseudo-random noise(“PN”) code sequence as a spread spectrum signal. The subscriber'stransmitter and the receiving base station share the code, which is usedto distinguish the subscriber from other subscribers in the system, whouse different codes PN codes. Thus, a CDMA system uses codes rather thanfrequency and/or time slots to provide multiple access.

The total capacity of a multiple access system may be further improvedby dividing a wireless system into cells and, in the case of FDMA andTDMA, using only different frequency channels in adjoining cells. Theorganization of message paging and cellular telephone systems into cellsis widely known and understood. Division into cells is accomplished bylimiting the transmission range of both the base stations and the mobilecommunication units. The frequencies used in one cell do not interferewith the different frequencies used in the adjoining cells and are nottransmitted far enough to interfere with identical frequencies used inmore remote, non-adjoining cells. Frequency “reuse” is thereforepossible by dividing a TDMA or FDMA system into cells.

In the case of CDMA, division of the system into cells does not affectfrequency allocation, since all subscribers use the same amount ofspectrum. However, there are less subscribers per cell in smaller cells,so there is less interference to distort the signal transmitted by eachsubscriber. Thus, capacity is still improved for the overall system.

The structure of a message paging system is somewhat different thancellular telephone systems. In a message paging system, all of the basestation transmitters throughout a wide coverage area are synchronizedand simultaneously broadcast (i.e., simulcast) a paging message in aforward-channel to a subscriber's pager. This simulcast increases thelikelihood that the paging message will reach the pager even throughobstacles, such as buildings. The paging system does not assign thesubscriber to a cell and transmit to the subscriber only in that cell,as in the case of a cellular telephone system.

However, even in a paging environment, there is a breakdown of themessage paging system into cells. That is, due to the low power of ahand-held two-way pager, a message transmitted by a user in areverse-channel has a very limited range compared to the base stationtransmitters. Therefore, a relatively large number of base stationreceivers must be deployed throughout the message paging system coveragearea in order to ensure that the signal transmitted by any pager isreceived by a base station receiver. As a result, minimizing the numberof receivers necessary to monitor the coverage area of a message pagingsystem becomes an important consideration. Using less receivers lowersthe infrastructure cost and, therefore, lowers the service cost tosubscribers.

There exists a need in the art for an improved wireless communicationsystem that minimizes the equipment cost necessary to operate thesystem. In particular, there is a need for an improved wirelessmessaging system that minimizes the number of base station receiversrequired to operate the system. There is a further need in the art foran improved narrowband messaging system capable of providing advancedtwo-way messaging services that maximizes frequency reuse and spectralefficiency with a minimum number of base station receivers.

SUMMARY OF THE INVENTION

The limitations inherent in the prior art described above are overcomeby an improved base station for communicating with mobile communicationunits (e.g., message pagers, PCS devices, personal data assistant andother processing systems that include wireless communicationfunctionality) in a wireless messaging system. In an advantageousembodiment, the base station includes: 1) a transmitter that is capableof transmitting messages to the communication units in a forward-channelhaving a first frequency range; 2) a receiver that is capable ofreceiving messages from the communication units in a reverse-channelhaving a second frequency range; and 3) an antenna that is capable oftransmitting the forward-channel messages at a first angle of electricaldowntilt below the horizon and receiving the reverse-channel messages ata second angle of electrical downtilt, wherein the second angle ofelectrical downtilt is less than the first angle of electrical downtilt.

According to an advantageous embodiment, the first angle of electricaldowntilt is determined by the first frequency range and the second angleof electrical downtilt is determined by the second frequency range. Aswill be discussed in detail herebelow, the downtilt angle of a receivebeam is preferably slightly below the horizon. Use of a relatively smallangle of electrical downtilt in the reverse-channel allows the antennato focus on signals from more distant communication units, includingthose beyond the boundaries of the coverage area in which the basestation resides. This tends to increase the probability that the antennawill receive reverse-channel signals from communication units in othercoverage areas, thereby increasing the overall macro-diversity of theantenna in the messaging network.

In an alternate embodiment of the present invention, the base stationfurther comprises an amplifier disposed proximate the antenna foramplifying messages received in the reverse-channel prior to processingin the receiver. In a related embodiment, the antenna is a sectoredantenna that is operable to transmit a forward-channel message in aselected direction at greater signal strength relative to a signalstrength transmitted in a non-selected direction. In another relatedembodiment, the antenna is a sectored antenna operable to amplify areverse-channel message received from a selected direction and attenuatea reverse-channel message received from a non-selected direction.

In another alternate embodiment of the present invention, the secondangle of electrical downtilt is approximately zero degrees, such thatthe antenna is optimized to receive reverse-channel messages from remotecommunication units.

The foregoing SUMMARY OF THE INVENTION outlines, rather broadly, someadvantageous features of various embodiments of the present invention sothat those of ordinary skill in the art may better understand theDETAILED DESCRIPTION that follows. Additional features of the inventionwill be described hereafter that form the subject matter of the CLAIMSOF THE INVENTION. Those of ordinary skill in the art should appreciatethat they can readily use the disclosed conception and specificembodiments as a basis for designing or modifying other structures forcarrying out the same purposes of god the present invention. Those ofordinary skill in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentinvention in its broadest form.

Before undertaking the DETAILED DESCRIPTION, it may be advantageous toset forth definitions of certain words and phrases used throughout thispatent document: the terms “include” and “comprise,” as well asderivatives thereof, mean inclusion without limitation; the term “or,”is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, be a property of, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, wherein like numbers designate like objects andin which:

FIG. 1 illustrates a representative portion of a conventional messagepaging network in accordance with the PRIOR ART;

FIG. 2 illustrates conventional forward and reverse-channels associatedwith a base station antenna using electrical downtilt techniques inaccordance with the PRIOR ART;

FIG. 3 illustrates forward and reverse-channels associated with a basestation in accordance with an exemplary embodiment of the presentinvention;

FIG. 4 illustrates an improved messaging network implementing improvedbase stations and an improved receiver in accordance with an exemplaryembodiment of the present invention;

FIG. 5 illustrates an improved messaging network implementing improvedbase stations in accordance with a second exemplary embodiment of thepresent invention; and

FIG. 6 illustrates a flow diagram of an exemplary method for operatingthe improved base station of FIGS. 3 to 5 in accordance with theprinciples of the present invention.

DETAILED DESCRIPTION

Turning initially to FIG. 1, illustrated is a representative portion ofa conventional message paging network (generally designated 100;hereafter, referred to as “messaging network 100”) in accordance withthe PRIOR ART. Messaging network 100 may provide, for example, two-wayvoice and text messages to subscribers. Messaging network 100 isrepresented by three exemplary fixed land sites, called base stations,for communicating with a plurality of mobile communication units (e.g.,message pagers, PCS devices, personal data assistant and otherprocessing systems that include wireless communication functionality,etc.) within messaging network 100. Base stations 111, 112 and 113, eachlabeled “BS” in FIG. 1, have coverage areas 101, 102, and 103,respectively, that are determined by the power of the transmitters inbase stations 111, 112, and 113. For the, purposes of illustration anddiscussion, coverage areas 101, 102, and 103 are shown as circles. Inreal world environments, however, each of coverage areas 101, 102, and103 may differ significantly from an idealized circular form.

For purposes of illustration, a plurality of message paging units, eachlabeled “P” in FIG. 1, are shown scattered throughout messaging network100. Paging units 121 and 122 are located within coverage area 101 andmay engage in two-way messaging with base station 111. Paging units 123and 124 are located in coverage area 102 and may engage in two-waymessaging with base station 112. Paging units 126, 127 and 128 arelocated in coverage area 103 and may engage in two-way messaging withbase station 113. Paging unit 125 is in coverage areas 102 and 103 andmay engage in two-way messaging with base stations 112 and 113.

In a narrowband messaging environment, such as FDMA, base stations 111,112, and 113 transmit RF signals in a forward-channel, such as from939-940 MHz, for example. Base stations 111, 112, and 113 receive RFsignals in a reverse-channel at, for example, 901-902 MHz. Each basestation is effectively a transceiver that contains an RF transmitter andan RF receiver for carrying out two-way communications. Each paging unitreceives forward-channel messages directed to it at a selected frequencywithin the forward-channel. Each paging unit also transmitsreverse-channel messages at a selected frequency within thereverse-channel.

Messaging network 100 may be, for example, a two-way wireless messagingsystem compatible with the MOTOROLA® ReFLEX™ transport protocol. TheReFLEX™ protocol may be used to send a numeric message, such as aconventional 10-digit telephone number, to a paging unit. The pagingunit may then transmit in the reverse channel an automaticacknowledgment message that does not require subscriber action.Alternatively, the ReFLEX™ protocol may be used in an enhanced pagingmode to send a more complex alphanumeric message, such as an e-mail textmessage, to the paging unit. The pager may then transmit in thereverse-channel an automatic acknowledgment message that does notrequire subscriber action. Some time later the subscriber may transmit a“canned” message stored in the paging unit, such as “Will Call YouLater”, or a unique message composed by the subscriber. Additionally,the paging unit may be enabled to transmit or receive voice messages ofshort duration recorded by the subscriber or a caller.

Base station 111 transmits data and voice messages to paging units incoverage area 101; base station 112 transmits data and voice messages topaging units in coverage area 102; and base station 113 transmits dataand voice messages to paging units in coverage area 103. Base stations111, 112, and 113 may be connected to one another and to a centralcontrol facility (not shown) by a wired backbone, such as a proprietaryfiber-optic network. In alternate embodiments, base stations 111, 112,and 113 may be connected to one another and to a central controlfacility by a satellite communications link, such as through a verysmall aperture terminal (“VSAT”).

Voice and text paging messages may be received into the central controlfacility from a variety of sources. Some messages may be received fromthe public telephone system in the form of simple call-back numbersentered by a caller on a DTMF keypad. Alphanumeric messages may bereceived by the central control facility from an Internet connection.Additionally, voice messages from callers may be received from thepublic telephone system and recorded for subsequent transmission to thesubscriber.

As is well known, the transmit power of a base station is typically muchgreater than the transmit power of the paging units in each coveragearea. In order to maximize the probability of receiving areverse-channel message from a paging unit, additional receive-onlystations, or simply receivers, are frequently disposed throughoutmessaging network 100 in order to decrease the average distanceseparating a paging unit from the nearest paging system receiver. Theextra receivers thereby minimize the effects of multi-path fading, delayspread, and signal blocking with respect to each paging unit. Thereceivers are also connected to the base stations and the centralcontrol facility by a wired proprietary. data link.

For example, receivers 131 and 132 are located in coverage area 101 andrelay messages received in the reverse-channels from any of the pagingunits in messaging network 100 to the central control facility.Similarly, receivers 133 and 134, located in coverage area 102, receivemessages in the reverse-channel from any of the paging units inmessaging network 100 and relay the messages to the central controlfacility. Finally, receivers 135 and 136 in coverage area 103 relaymessages received in the reverse-channel to the central controlfacility.

Because of the plurality of receivers in each coverage area, includingany receiver that may be part of the base station, a message transmittedby a paging unit may be received by more than one receiver. Thus, if thesignal received by one receiver experiences multi-path fading or isblocked by a structure, such as a building, another receiver can stillreceive the signal and relay it to the base station for processing.

Receivers are not tied to a particular coverage area. All receiversrelay the reverse-channel signal that is received to the central controlfacility. For example, paging units 125 and 126 are located proximatereceiver 135 in coverage area 103. Messages transmitted by paging units125 and 126 may be received by receiver 135, as well as base stations112 and 113 in coverage areas 102 and 103, respectively. This built-inredundancy is known as antenna diversity.

Many receiver systems actually comprise a pair of receive paths coupledto two local diverse antenna systems. In such a “micro-diversity”system, both receive paths transfer the received signal energy from areverse-channel message to the local receiver circuitry at the basestation, which then performs error-bit checking to determine if eitherof the two signals was well-received. If both of the receivedreverse-channel signals contain errors as a result of fading orobstructions, the receiver circuitry can sum the energies of both of thereceived signals to form a composite signal. The composite signal maythen be error checked to determine the reverse-channel message.

The base stations and receivers in messaging network 100 employ avariety of conventional techniques to prevent interference between thesignals transmitted by the base stations and the signals transmitted bythe paging units. In a FDMA-based narrowband PCS messaging system, onelevel of protection is provided by the frequency filtering thatseparates signals according to their transmission frequency. Messagingnetwork 100 may also employ a sector antenna multiple receiver (“SAMR”)that focuses transmitted and received signals. For example, messagingnetwork 100 may employ a SAMR that uses three panel antennas, each ofwhich transmits a full strength signal into a 120 degree sector in theforward-channel, but transmits only an attenuated signal in theremaining 240 degrees of arc. Each panel antenna also amplifiesreverse-channel signals received from the 120 degree sector and filtersout signals or noise received from the remaining 240 degrees of arc.

Prior art paging systems such as messaging network 100 typically employelectrical “downtilt” in the antennas in the base stations and receiversin order to reduce the effective range of transmitted signals and toattenuate signals received from distant paging units or base stations.FIG. 2 illustrates conventional forward and reverse-channels associatedwith a base station antenna 202 using electrical downtilt techniques inaccordance with the PRIOR ART. Although the discussion that follows ofPRIOR ART electrical downtilt techniques centers on base station 111, itshould be noted that this is by way of illustration only, and that thefollowing discussion applies with equal force to the other base stationsand receivers in messaging network 100.

Base station 111 comprises a tower 201 for holding antenna 202 in anelevated position above the ground 205. Base station 111 also comprisesa transmitter 206 for transmitting messages in the forward-channel and areceiver 207 for receiving messages in the reverse-channel. The forwardand reverse-channel messages are appropriately transferred to or fromthe central control facility.

Reference beam 211 is a horizontal reference axis indicating therelative position of the horizon. Antenna 202 employs electricaldowntilt to transmit messages in the forward-channel along a transmitbeam 212. Transmit beam 212 represents the direction of travel withrespect to the horizon of the main power lobe transmitted by antenna202. As FIG. 2 indicates, transmit beam 212 is transmitted below thehorizon at a downtilt angle, θ1. The downtilt angle θ1 is determined bythe electrical characteristics of antenna 202 and is dependent on thetransmission frequency of the forward-channel.

Antenna 202 employs electrical downtilt to receive messages in thereverse-channel along a receive beam 213. Receive beam 213 representsthe direction of travel with respect to the horizon of an incidentsignal transmitted from a paging unit located at an optimum distanceaway from antenna 202. Antenna 202 has been optimized to amplify signalsreceived from paging units at the optimum distance. The downtilt angle,θ2, of receive beam 213 is below the horizon and is also below thedowntilt angle, θ1, of the transmit beam 212.

The primary purpose in employing electrical downtilt in transmit beam212 is to restrict the size of the coverage areas 101, 102 and 103 inpaging network 100. If transmit beam 212 were oriented directly towardsthe horizon with no electrical downtilt, much of the energy of thesignal transmitted by antenna 202 would be transmitted out to infinity,and therefore lost. Furthermore, employing only a small angle ofelectrical downtilt would direct the main power lobe of transmit beam212 towards very distant paging units in other coverage areas-resultingin a weak forward-channel messages being received in the distant pagingunits.

Electrical downtilt in the forward-channel sends a stronger signal torelatively near paging units located at the optimum distance fromantenna 202 (closer to the perimeter of the coverage area), whileminimizing the interfering forward-channel signal sent to relativelyremote paging units. Similarly, employing electrical downtilt in receivebeam 213 enables antenna 202 to amplify reverse-channel signals fromnearby paging units, while attenuating reverse-channel signals from moredistant paging units.

Because the downtilt angle, θ2, of receive beam 213 is below thedowntilt angle, θ1, of the transmit beam 212, antenna 202 is optimizedto receive reverse-channel signals that-are less distant than the pagingunits targeted by the transmit beam 212. It would appear that basestation 111 may be able to send messages in the forward-channel topaging units from which it cannot receive messages in thereverse-channel. However, it must be remembered that the receivercircuitry in the base station 111 is far more sensitive than thereceiver circuitry in the paging units and that coverage area 101 alsocontains a plurality of receive-only stations, including receivers 131and 132, that also receive reverse-channel signals. The number andpositions of the receivers in messaging network 100 is selected toensure sufficient overlap of receiver coverage areas. A signal from anypaging unit in messaging network 100 is therefore fairly assured ofbeing received by two or three nearby receivers.

The electrical downtilt and antenna diversity techniques described abovein connection with messaging network 100 are costly in terms ofhardware. A large number of receivers are required to provide effectivereverse-channel coverage throughout messaging network 100. The presentinvention provides an improved messaging network that implements a muchlower ratio of receivers to transmitters across the messaging network.

Turning now to FIG. 3, illustrated are forward and reverse-channelsassociated with a base station 301 in accordance with an exemplaryembodiment of the present invention. The base station 301 comprises atower 302 for holding an antenna 303 in an elevated position aboveground 205. The base station 301 also comprises a transmitter 306 fortransmitting messages in the forward-channel and a receiver 307 forreceiving messages in the reverse-channel. The forward andreverse-channel messages are appropriately transferred to or from thecentral control facility (not shown). A tower-top amplifier 304 mayoptionally be included to strengthen received signals at the antenna 303before relaying the received signals to the receiver 307, in order tocompensate for line losses occurring on long cables between the antennaand the receiver.

Although the remainder of the discussion of the exemplary embodimentfocuses on base station 301, it should be noted that this is by way ofillustration only, and that the following discussion applies with equalforce to the other base stations and receivers in the improved messagingnetwork.

Reference beam 311 is a horizontal reference axis indicating therelative position of the horizon. Antenna 303 employs electricaldowntilt to transmit messages in the forward-channel along a transmitbeam 312. Transmit beam 312 represents the direction of travel withrespect to the horizon of the main power lobe transmitted by antenna303. As FIG. 3 indicates, transmit beam 312 is transmitted below thehorizon at a downtilt angle, θ1. The downtilt angle, θ1, is determinedby the electrical characteristics of antenna 303 and is dependent on thetransmission frequency of the forward-channel.

Antenna 303 employs electrical downtilt to receive messages in thereverse-channel along a receive beam 313. Receive beam 313 representsthe direction of travel with respect to the horizon of an incidentsignal transmitted from a paging unit located at an optimum distanceaway from antenna 303. Antenna 303 has been optimized to amplify signalsreceived from paging units at the optimum distance. The downtilt angle,θ2, is determined by the electrical characteristics of antenna 303 andis dependent on the transmission frequency of the reverse-channel.

However, unlike the PRIOR ART antenna 202, the downtilt angle, 62, ofthe receive beam 313 is now above the downtilt angle, θ1, of thetransmit beam 312. Furthermore, in a preferred embodiment of the presentinvention, the downtilt angle, θ2, of receive beam 313 is only slightlybelow the horizon. In other embodiments of the present invention, thedowntilt angle, θ2, of receive beam 313 may be oriented directly at thehorizon. The use of a smaller angle of electrical downtilt in thereverse-channel in antenna 302 focuses antenna 303 on signals from moredistant paging units, including those beyond the boundaries of thecoverage area in which base station 301 resides. This type ofoptimization increases the probability that antenna 303 will receivereverse-channel signals from remote paging units in other coverageareas, thereby increasing the overall macro-diversity of the antennas inthe paging network.

The present invention optimizes antenna 303 for the amplification ofsignals from remote paging units, and thereby maximizes antennamacro-diversity effects, under the assumption that, although antenna 303may occasionally lose the signal from a nearby paging unit due toblocking or multipath fading, at least one other less-close antenna willproperly receive the lost paging unit's signal because the less-closeantenna has also been optimized to amplify the signal of remote pagingunits. Maximizing the ability of more remote receivers to receive thepaging unit's transmission improves the overall performance of thepaging network.

Turning next to FIG. 4, illustrated is an improved messaging network(generally designated 400) implementing improved base stations 411, 412and 413 and an improved receiver 421 in accordance with an exemplaryembodiment of the present invention. Base stations 411, 412 and 413,each labeled “BS” in FIG. 4, have coverage areas 401, 402, and 403,respectively, that are determined by the power of the transmitters inbase stations 411, 412, and 413. For the purposes of illustration anddiscussion, coverage areas 401, 402, and 403. are shown as circles. Inreal world environments, however, each of coverage areas 401, 402, and403 may again differ significantly from an idealized circular form.

Each of base stations 411, 412, and 413 communicates with a plurality ofpaging units generally located within its coverage area. Under ordinarycircumstances, base station 411 transmits data and voice messages topaging units in coverage area 401; base station 412 transmits data andvoice messages to paging units in coverage area 402; and base station413 transmits data and voice messages to paging units in coverage area403. Base stations 411, 412, and 413 are connected to one another and acentral control facility (not shown) by a wired backbone, such as aproprietary fiber-optic network or, preferably, by a wireless link, suchas a two-way VSAT network.

A plurality of paging units are shown scattered throughout messagingnetwork 400. Paging units 121 and 122 are located within coverage area401 and may be in two-way communication with at least base station 411.Paging units 123, 124 and 125 are located in coverage area 402 and maybe in two-way communication with at least base station 412. Paging units126, 127 and 128 are located in coverage area 403 and may be in two-waycommunication with at least base station 413.

As in the PRIOR ART network, each of base stations 411, 412 and 413transmit data and voice messages in a forward-channel to the pagingunits within its associated coverage area. Each base station may alsoreceive messages in a reverse-channel from any paging unit in messagingnetwork 400. Each base station is effectively a transceiver thatcontains an RF transmitter and an RF receiver for carrying out two-waycommunications. As in the case of the PRIOR ART messaging network 100,the two-way message traffic in messaging network 400 may comprise voiceand data messages associated with one of a plurality of information ornotification modes, such as numeric and alphanumeric paging and voicemessaging. In an advantageous embodiment, messaging network 400 is aFDMA-based narrowband messaging system implementing the MOTOROLA® ReFLEX25® protocol and employing sector antenna multiple receiver (“SAMR”)systems that focus transmitted signals in the forward-channel andamplify received signals in the reverse-channel.

Messaging network 400 also comprises an additional receive-only stationto receive messages in the reverse-channel. The receive-only station,receiver 421, is connected to the base stations and a central controlfacility (not shown) by a wired backbone, such as a proprietaryfiber-optic network. It can now be seen, however, that the total numberof receivers required by messaging network 400, including the receiversin base stations 401, 402, and 403, is much less than in the PRIOR ARTmessaging network 100. This is due to the macro-diversity effect gainedacross the entirety of messaging network 400 by optimizing theelectrical downtilt of the antennas in improved base stations 411, 412and 413 and in improved receiver 421 according to the exemplary antennasystem described in FIG. 3.

Turning next to FIG. 5, illustrated is an improved messaging network 500implementing improved base stations 511-514 in accordance with a secondexemplary embodiment of the present invention. The electrical downtiltof each of the antennas in improved base stations 511-514 is alsooptimized according to the antenna system described in FIG. 3. Theexemplary messaging network 500 is optimized for use in a heavy urbanarea. The outline of a large cluster of office buildings or a densemetropolitan area is denoted by perimeter 501.

Base stations 511-514 are located around perimeter 501. Receive-onlystations optimized in accordance with the antenna system described inFIG. 3 may also be implemented within the urban core, if the density ofpaging receivers and the number of signal-blocking obstacles sorequires. Paging units 521, 522 and 523 are located in the dense urbanarea and may be in two-way communication with at least one of basestations 511-514. In the forward-channel, base stations 511-514 transmitmessages into the dense urban area and take advantage of reflections offbuildings to ensure that the forward-channel signal reaches the intendedpaging unit. Similarly, in the reverse-channel, base stations 511-514can receive signals reflected off buildings to ensure that at least oneof the base stations receives a reverse-channel message transmitted byany one of the paging units 521, 522, and 523.

Turning lastly to FIG. 6, a flow diagram of an exemplary method(generally designated 600) for operating the improved base station 411in accordance with the principles of the present invention. For thepurpose of illustration, messaging network 400 is assumed to be, forexample, a two-way wireless messaging'system compatible with theMOTOROLA® ReFLEX™ transport protocol. In a normal operating mode, basestation 411 continually receives from the central control facilityforward-channel messages to be broadcast (or simulcast) to paging unitsin messaging network 400 and synchronization signals which synchronizethe simultaneous transmission of the forward-channel messages to theappropriate pagers (process step 601). In the illustrated example, basestation 411 receives a message that is to, be transmitted in theforward-channel to Pager X.

Next, at the designated time, the transmitter 306 in base station 411transmits the queued forward-channel messages to each pager, includingthe forward-channel message to Pager X (process step 602). All of theforward-channel messages are transmitted by all of the base stations atan electrical downtilt angle of 91. This simulcast of each message pageby every base station in messaging network 400 maximizes the probabilitythat each paging message reaches the targeted paging unit. Theforward-channel message also includes information telling a receivingpaging unit, such as Pager X, the reverse-channel time slot andfrequency in which the receiving pager should transmit any scheduledmessages, such as the automatic acknowledgment message each paging unitsends upon receipt of the forward-channel message.

In the reverse-channel, the receiver 307 in base station 411 monitorsthe early time slots 0-17 and selected frequency in each reverse-channelframe to detect the automatic acknowledgment message that Pager X isscheduled to send back upon receipt of the forward-channel message(process step 603). The receiver antenna is optimized at an electricaldowntilt angle of θ2 to receive the reverse-channel messages transmittedby relatively remote paging units in the messaging network 400. Next,the receiver 307 in base station 411 monitors the late time slots 18-22and selected frequency in each reverse-channel frame to detectunscheduled messages from Pager X (process step 604). An unscheduledreverse-channel message may include the registration request generatedby a paging unit when it is first powered on and identifies itself tomessaging network 400. Alternatively, an unscheduled reverse-channelmessage may include an Inbound Message Request whereby Pager X informsmessaging network 400 that the subscriber wishes to send a voice oralphanumeric message that subscriber has composed.

Next, base station 411 sends all reverse-channel messages to the centralcontrol facility for further processing (process step 605). At thispoint, the base station 411 may repeat the process described above fromthe start.

As is apparent from the foregoing, the principles of the presentinvention are particularly beneficial when applied to wirelesscommunication networks that employ simulcast messaging. Those skilled.in the art should understand that although message pager have been usedto illustrate the principles of the present invention, alternatecommunication units (or devices) may suitably be used with a messagingsystem in accordance with the principles of the present invention. Forinstance, PCS devices, as well as suitably arranged calculators;palmtop, laptop, notebook, personal or other computers; and any otherlike processing systems, including PDAs (i.e., devices, or “gadgets,”that perform particular tasks, such as a diary, database, PCS, messagepaging, multimedia player, memo-taker, calculator, alarm clock, etc.).

Although the principles of the present invention have been described indetail with reference to message paging system and infrastructureembodiments, those of ordinary skill in the art should understand thatthey can make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the invention in itsbroadest form.

What is claimed is:
 1. For use in a wireless messaging system, a basestation that communicates with communication units located in saidwireless messaging system, said base station comprising: a transmitterthat transmits messages to said communication units in aforward-channel; a receiver that receives messages from saidcommunication units in a reverse-channel; and an antenna that transmitssaid forward-channel messages at a first angle of electrical downtiltbelow horizon and receives said reverse-channel messages at a secondangle of electrical downtilt, wherein said second angle of electricaldowntilt is less than said first angle of electrical downtilt and saidantenna is a sectored antenna that is operable to transmit aforward-channel message in a selected direction at greater signalstrength relative to a signal strength transmitted in a non-selecteddirection.
 2. The base station set forth in claim 1 wherein saidsectored antenna is further operable to amplify a reverse-channelmessage received from a selected direction and attenuate areverse-channel message received from a non-selected direction.
 3. Thebase station set forth in claim 1 wherein said first angle of electricaldowntilt is determined by a first frequency range.
 4. The base stationset forth in claim 1 wherein said second angle of electrical downtilt isdetermined by a second frequency range.
 5. The base station set forth inclaim 1 further comprising an amplifier disposed proximate said antennathat is capable of amplifying messages received in said reverse-channelprior to processing in said receiver.
 6. The base station set forth inclaim 1 wherein said second angle of electrical downtilt isapproximately zero degees, such that said antenna is optimized toreceive reverse-channel messages from remote communication units.
 7. Awireless messaging system that communicates with communication unitscomprising: a plurality of transmitter stations wherein at least ones ofsaid plurality of transmitter stations comprises: a transmitter thattransmits messages to said communication units in a forward-channel; areceiver that receives messages from said communication units in areverse-channel; and antenna means for transmitting said forward-channelmessages at a first angle of electrical downtilt below horizon andreceiving said reverse-channel messages at a second angle of electricaldowntilt, wherein said second angle of electrical downtilt is less thansaid first angle of electrical downtilt.
 8. The wireless messagingsystem set forth in claim 7 wherein said antenna means is a sectoredantenna that is operable to transmit a forward-channel message in aselected direction at greater signal strength relative to a signalstrength transmitted in a non-selected direction.
 9. The wirelessmessaging system set forth in claim 8 wherein said sectored antenna isfurther operable to amplify a reverse-channel message received from aselected direction and attenuate a reverse-channel message received froma non-selected direction.
 10. The wireless messaging system set forth inclaim 7 wherein said first angle of electrical downtilt is determined bya first frequency range.
 11. The wireless messaging system set forth inclaim 7 wherein said second angle of electrical downtilt is determinedby a second frequency range.
 12. The wireless messaging system set forthin claim 7 further comprising an amplifier disposed proximate saidantenna that is capable of amplifying messages received in saidreverse-channel prior to processing in said receiver.
 13. The wirelessmessaging system set forth in claim 7 wherein said second angle ofelectrical downtilt is approximately zero degrees, such that saidantenna is optimized to receive reverse-channel messages from remotecommunication units.
 14. A method of operating a wireless messagingsystem to communicate messages with communication units located in saidwireless messaging system, said method comprising the steps of:transmitting messages to the communication units in a forward-channeland at a first angle of electrical downtilt below horizon; receivingmessages from the communication units in a reverse-channel and at asecond angle of electrical downtilt, wherein the second angle ofelectrical downtilt is less than the first angle of electrical downtilt;and amplifying a reverse-channel message received from a selecteddirection and attenuating a reverse-channel message received from anon-selected direction.
 15. The method set forth in claim 14 wherein thefirst angle of electrical downtilt is determined by a first frequencyrange.
 16. The method set forth in claim 14 wherein the second angle ofelectrical downtilt is determined by a second frequency range.
 17. Themethod set forth in claim 14 wherein the step of transmitting furtherincludes the step of transmitting forward-channel messages in a selecteddirection at greater signal strength than forward-channel messagestransmitted in a non-selected direction.
 18. A wireless communicationsystem that includes a plurality of associated base stations operable tosimulcast messages to communication units in a forward-channel and toreceive messages from ones of said communication units in areverse-channel, said forward-channel messages simulcast at a firstangle of electrical downtilt and said reverse-channel messages receivedat a second angle of electrical downtilt, said second angle ofelectrical downtilt being less than said first angle of electricaldowntilt, and wherein at least one of said base stations includes asectored antenna that transmits a forward-channel message in a selecteddirection at greater signal strength relative to a signal strengthtransmitted in a non-selected direction.
 19. The wireless communicationsystem set forth in claim 18 wherein said sectored antenna is operableto amplify a reverse-channel message received from a selected directionand attenuate a reverse-channel message received from a non-selecteddirection.
 20. The wireless communication system set forth in claim 18wherein said first angle of electrical downtilt is determined by a firstfrequency range.
 21. The wireless communication system set forth inclaim 18 wherein said second angle of electrical downtilt is determinedby a second frequency range.
 22. The wireless communication system setforth in claim 18 wherein one of said base stations includes anamplifier that amplifies messages received in said reverse-channel. 23.The wireless communication system set forth in claim 18 wherein saidsecond angle of electrical downtilt is approximately zero degrees, suchthat an antenna is optimized to receive reverse-channel messages fromremote communication units.
 24. The wireless communication system setforth in claim 18 wherein said base stations are associated with aperimeter of an urban area.
 25. A method of operating a wirelesscommunication system that includes a plurality of associated basestations capable of simulcasting messages to communication units in aforward-channel and receiving messages from ones of said communicationunits in a reverse-channel, said method comprising the cooperative stepsof: simulcasting said forward-channel messages at a first angle ofelectrical downtilt; receiving said reverse-channel messages at a secondangle of electrical downtilt, wherein said second angle of electricaldowntilt being less than said first angle of electrical downtilt; andusing a sectored antenna to transmit a forward-channel message in aselected direction at greater signal strength relative to a signalstrength transmitted in a non-selected direction.
 26. The method ofoperation set forth in claim 25 further comprising the step of furtheramplifying a reverse-channel message received from a selected directionand attenuating a reverse-channel message received from a non-selecteddirection.
 27. The method of operation set forth in claim 20 whereinsaid first angle of electrical downtilt is determined by a firstfrequency range.
 28. The method of operation set forth in claim 27wherein said second angle of electrical downtilt is determined by asecond frequency range.
 29. The method of operation set forth in claim27 further comprising the step of amplifying messages received in saidreverse-channel.
 30. The method of operation set forth in claim 27wherein said second angle of electrical downtilt is approximately zerodegrees, such that an antenna is optimized to receive reverse-channelmessages from remote communication units.
 31. The method of operationset forth in claim 27 further comprising the step of associating saidbase stations with a perimeter of an urban area.
 32. For use in a basestation that communicates with communication units located of a wirelessmessaging system, an antenna that transmits forward-channel messages ata first angle of electrical downtilt below horizon and receivesreverse-channel messages at a second angle of electrical downtilt,wherein said second angle of electrical downtilt is less than said firstangle of electrical downtilt and said antenna is a sectored antenna thatis operable to transmit a forward-channel message in a selecteddirection at greater signal strength relative to a signal strengthtransmitted in a non-selected direction.
 33. The antenna set forth inclaim 32 wherein said base station comprises (i) a transmitter thattransmits messages to said communication units in a forward-channel, and(ii) a receiver that receives messages from said communication units ina reverse-channel.
 34. The antenna set forth in claim 33 furthercomprising an amplifier that is capable of amplifying messages receivedin said reverse-channel prior to processing in said receiver.
 35. Theantenna set forth in claim 32 is further operable to amplify areverse-channel message received from a selected direction and attenuatea reverse-channel message received from a non-selected direction. 36.The antenna set forth in claim 33 wherein said first angle of electricaldowntilt is determined by a first frequency range.
 37. The antenna setforth in claim 36 wherein said second angle of electrical downtilt isdetermined by a second frequency range.
 38. The antenna set forth inclaim 32 wherein said second angle of electrical downtilt is optimizedto receive reverse-channel messages from remote communication units. 39.A method of operating a sectored antenna for use in a base station thatcommunicates with communication units located of a wireless messagingsystem, said sectored antenna operable to (i) transmit forward-channelmessages at a first angle of electrical downtilt below horizon and (ii)receive reverse-channel messages at a second angle of electricaldowntilt, said second angle of electrical downtilt is less than saidfirst angle of electrical downtilt, said method of operating saidsectored antenna comprising the step of transmitting a forward-channelmessage in a selected direction at greater signal strength relative to asignal strength transmitted in a non-selected direction.
 40. The methodof operating said sectored antenna set forth in claim 39 wherein saidbase station comprises (i) a transmitter that transmits messages to saidcommunication units in a forward-channel, and (ii) a receiver thatreceives messages from said communication units in a reverse-channel,and said method of operating said sectored antenna further comprises thestep of amplifying messages received in said reverse-channel prior toprocessing in said receiver.
 41. The method of operating said antennaset forth in claim 39 further comprising the steps of: amplifying areverse-channel message received from a selected direction; andattenuating a reverse-channel message received from a non-selecteddirection.
 42. The method of operating said antenna set forth in claim39 further comprising the step of determining said first angle ofelectrical downtilt by a first frequency range.
 43. The method ofoperating said antenna set forth in claim 42 further comprising the stepof determining said second angle of electrical downtilt by a secondfrequency range.
 44. The method of operating said antenna set forth inclaim 39 further comprising the step of optimizing said second angle ofelectrical downtilt to receive reverse-channel messages from remotecommunication units.